1. Field of the Invention
This invention relates generally to humidity sensors. More particularly, it relates to an apparatus and technique providing a more accurate, reliable and cost effective humidity sensor than is conventionally available.
2. Background of Related Art
Long term ambient humidity measurement is difficult to achieve with any high degree of accuracy or reliability.
Previous humidity sensors typically use mechanisms including delicate moving parts and materials having variable properties. One example of such a humidity sensor includes the use of a bundle of hair (e.g., blond human hair). Another is a coil enveloped in hydroscopic paper which expands/contracts with humidity. Such humidity sensors typically exhibit low measurement accuracy, particularly at the extremes of 0-20% and 80-100% humidity.
Humidity sensors having higher accuracy exist, but typically at the cost of higher maintenance and short accuracy lifetimes in the field. For instance, a humidity sensor using a chilled mirror is known wherein the mirror is chilled to the dew point which, along with the temperature, provides a fairly accurate humidity measurement. However, such higher accuracy humidity sensors , including lithium chloride and wet/dry bulb automated, are typically expensive to manufacture and require rigid and frequent maintenance (e.g., to clean the mirror).
Perhaps the more popular type of humidity sensor are solid state humidity sensors. While solid state humidity sensors are reasonably priced and accurate, they have been known to fail or degrade fairly quickly (e.g., after about 1 year or so), and thus tend to be both inaccurate and somewhat unreliable after a period of time.
Accordingly, there is a need for a humidity sensor which is accurate not only at a nominal humidity level but also at the extreme measurement levels, which is reliable, and which requires minimal if any maintenance.